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Acyclovir is primarily used to treat infections caused by the herpes simplex virus (HSV), such as genital herpes, cold sores, and shingles (herpes zoster).

Last Modified: 21 May 2024

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What is Acyclovir? 

Acyclovir (also spelt as Aciclovir) is an antiviral medication that effectively treats various types of infections mainly caused by the herpes simplex virus (HSV). This drug works by interfering with the replication process of the viral DNA, hindering the virus's ability to multiply and spread. Its active ingredient is acyclovir itself, a synthetic nucleoside analogue. 

Acyclovir is a synthetic compound with a molecular structure designed to mimic the building blocks of DNA, allowing it to integrate into the viral DNA chain. The drug is made through a complex chemical synthesis process that ensures a high degree of purity and stability. 

The generic name for this medication is acyclovir, and it is available under several brand names, including Zovirax, Sitavig, and others. 

Global Name

Acyclovir, also known as Aciclovir, is known by several brand names globally as listed below.  

Generic Name and Brand Names 

  • Generic name: Acyclovir
  • Brand names: Zovirax, Sitavig, and others.


What is Acyclovir used for?

Acyclovir is primarily used to treat infections caused by the herpes simplex virus (HSV), such as genital herpes, cold sores, and shingles (herpes zoster). It can also be used to prevent recurrent outbreaks of these infections. Other uses include treatment of infections with Epstein-Barr virus and to prevent cytomegalovirus (CMV) infection in transplant patients. 

How do you use Acyclovir?


  • Ophthalmic (eye) ointment 
  • Dermatologic (skin) cream 
  • Oral: Tablets, capsules, suspension 
  • Injectable solution for intravenous use 

Dosage information for Acyclovir varies based on the type of infection being treated: 

  • For genital herpes: Initial treatment - 200 mg taken five times a day by mouth for 10 days or 400 mg three times a day for 7-10 days; pls. seek consult for recurrent infection. 
  • For shingles: 800 mg taken five times by mouth a day for 7-10 days. 
  • For cold sores: 400 mg taken 3 times daily by mouth for 5-10 days. 
  • For Varicella Zoster (VZ, chickenpox): Acute treatment: 800 mg 5 times daily by mouth for 7-10 days 

Suitability across age groups: 

  • Children: Pediatric dosages are determined by a doctor based on weight and age. 
  • Adults: Follow prescribed dosages as mentioned above. 
  • Elderlies: May require dosage adjustment due to kidney function considerations. 
  • Pregnancy and Lactation (Breastfeeding/nursing mothers): 
  • Pregnancy – general safe to use as directed by your physician (US FDA category B drug) 
  • Lactation – generally safe to use as directed by your physician (American Academy of Pediatrics; UK Drugs in Lactation Advisory Service (UKDILAS)) 

Individuals who should not take Acyclovir: 

  • Those with hypersensitivity to acyclovir or valacyclovir. 
  • Those with certain pre-existing conditions as advised by a healthcare provider. 

Allergies and contraindications: 

  • Known allergy to acyclovir or any ingredients in the formulation. 

Warnings and precautions: 

  • Stay hydrated to prevent kidney issues. 
  • Take with or without food, but consistency can help reduce stomach upset. 

Interactions and contraindications: 

  • Can interact with drugs affecting kidney function. 
  • It may have additive effects with other nephrotoxic drugs. 

Side Effects

Common side effects may include nausea, diarrhoea, and headache. Severe side effects can include kidney problems and allergic reactions. 

Pharmacist Tips

  • Store at room temperature away from moisture and light. 
  • Do not touch or rub eyes after applying acyclovir cream to skin lesion to prevent eye infection. Wash hands immediately after topical application. 


Where is Acyclovir available in Hong Kong?

Acyclovir is a prescription medication that can be prescribed by healthcare providers.


Can Acyclovir prevent herpes transmission?

While Acyclovir reduces the risk of spreading herpes, it is not 100% effective in preventing transmission. 

Can you drink alcohol while taking Acyclovir? 

Acyclovir typically starts working within 24-48 hours, but it may take several days to observe significant symptom relief.

Is Acyclovir available to purchase over-the-counter?

No, Acyclovir is a prescription-only medication. 

How long does it take for Acyclovir to work?

Acyclovir typically begins to work within 24 to 48 hours of starting treatment, with symptoms like pain and healing of lesions often improving within a few days. The total duration for full effect can vary depending on the condition being treated and individual patient response.

This website provides content related to drug use and medicine for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Do not use the information on this website to diagnose or treat a health problem or disease without consulting a qualified healthcare provider. The website's owners and contributors are not liable for any repercussions, adverse effects, or consequences resulting from the use of any medication or information provided herein.

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